reader package

Package reader is the batch JSON read API for the frontend and the aggregator (design §2.5.6). It is private (re-deployable in place, no other realm may import it) and holds no state or money: everything comes from core, market and r/sys/users.

Every string goes out through safe.JSONWriter, so stored text can never forge a record (RA H-1: the old TSV reader split on tabs and newlines). Art is never batched: one token per Art call, because SVG rendering is what exhausted the query gas in nftread1 (RA L-9).